The present invention relates to a drill chuck. More particularly this invention concerns a lockable hammer-drill chuck.
A standard drill chuck has a chuck body rotatable about a chuck axis and formed centered on the axis with an axially forwardly open tool receiving hole and an array of axially extending guides opening axially forward into the hole. Respective externally toothed jaws axially displaceable in the guides mesh with an internally threaded actuating ring rotatable on the chuck body about the axis to axially displace the jaws in the respective guides. This ring bears axially backward on the chuck body via a roller bearing in turn riding on a support washer set in chuck body. A tightening sleeve is axially and rotationally coupled to the actuating ring so that when it is rotated about the chuck axis in a tightening direction, the jaws move together and when oppositely rotated in a loosening direction the jaws move apart.
As described in U.S. Pat. No. 5,765,839 of G. Rohm the tightening sleeve is mounted on the chuck body at its rear end by means of a washer set in the rear end of the sleeve and riding on a rearwardly directed shoulder of the chuck body. The tightening sleeve is, however, mainly fixed centrally on the locking ring so any axial forces working on the sleeve are transmitted via the bearing to the support washer. This construction allows most of the chuck parts to be made principally by turning for a relatively low manufacture cost and allows the overall length of the chuck to be minimized.
Such construction has the disadvantage that the tightening sleeve can rock somewhat on the chuck body with some play in particular at the front of the chuck. When canted somewhat, the tightening ring can be sufficiently offcenter that it produces vibration or radial throw when the chuck is rotated at high speed.
It is therefore an object of the present invention to provide an improved drill chuck.
Another object is the provision of such an improved drill chuck which overcomes the above-given disadvantages, that is where the tightening sleeve is solidly and immovably secured to the chuck body at least when the chuck is tightened on a tool.
A drill chuck has according to the invention a chuck body rotatable about a chuck axis and formed centered on the axis with an axially forwardly open tool receiving hole, an array of axially extending guides opening axially forward into the hole, a rear axially forwardly directed shoulder and a front axially forwardly directed shoulder. Respective externally toothed jaws axially displaceable in the guides mesh with an internally threaded actuating ring rotatable on the chuck body about the axis to axially displace the jaws in the respective guides. An elastically deformable support washer bears axially forward on the actuating ring and has an inner periphery bearing axially backward on the rear chuck-body shoulder. The washer in accordance with the invention bears on the rear chuck-body shoulder over a radial distance equal to at most one-half its radial dimension such that the support ring projects at least halfway from the chuck body, allowing its outer periphery to be deformed elastically backward on tightening of the chuck. A tightening sleeve axially and rotationally coupled to the actuating ring has a front axially rearwardly directed surface axially confronting the surface of the front chuck-body shoulder. The sleeve and ring are axially displaceable on rearward elastic deformation of the support washer from a position with the front shoulder surface out of contact with the front sleeve surface when the washer is generally undeformed and a position with the front sleeve surface bearing axially backward on the front shoulder surface when the washer is elastically rearwardly deformed.
Thus once this chuck is tightened, the support washer deforms and the surface at the front end of the tightening sleeve bears solidly axially backward on the front shoulder of the chuck body. This locks the sleeve solidly to the chuck body on center, so the chuck can be driven at high speeds without vibrating. On the other hand when not tightened, the tightening sleeve is solely carried by the locking ring so that it can be rotated easily. Furthermore the binding of the tightening sleeve on the chuck body gives an easily felt signal to the user that the chuck has been tightened sufficiently. At the same time such engagement prevents overtightening.
According to the invention the washer bears on the rear chuck-body shoulder over a radial distance equal to at most one-quarter the rear-shoulder radial dimension. This allows considerable deformation for smoothest possible operation.
A retaining washer set in the tightening sleeve bears axially forward on the actuating ring. This tightening sleeve includes a metallic outer sleeve part and a plastic inner sleeve part fixed in the outer part and in which the retaining washer is set. The retaining washer is axially rearward of the support washer. In addition the actuating ring includes a coupling ring having a rearwardly extending collar bearing axially rearward on the retaining washer. The mainly plastic tightening sleeve is quite light so that when subjected to sudden stops and starts its inertia will not be enough to loosen or tighten the chuck. Furthermore the softer inner part is somewhat compressible so that the chuck can be tightened smoothly.
In accordance with the invention at least one of the surfaces is constructed to increase the coefficient of friction thereof relative to the other of the surfaces. This effect can be achieved by a roughening of the one surface, by providing a soft friction-increasing coating on the one surface, by forming teeth on one or both of the surfaces, or by mounting a soft-friction-increasing washer between the surfaces. This friction washer is of a material having a higher coefficient of friction than either of the surfaces and can be axially displaceable on the chuck body. The surfaces are complementarily frustoconical and centered on the axis or are planar. Frustoconical surfaces ensure perfect centering of the tightening sleeve on the chuck body when the chuck is tightened.
A protective cap secured to the chuck body covers a front end of the tightening sleeve. In addition the chuck body is formed centered on the axis with an array of outwardly directed teeth. A coupling sleeve between the tightening sleeve and the chuck body is angularly fixed to the actuating ring and abutments on the tightening sleeve permit angular movement of the coupling sleeve relative to the tightening sleeve between a pair of end positions. A locking member angularly fixed on the coupling sleeve is displaceable between a locking position engaging the teeth and preventing rotation of the body relative to the coupling ring and a freeing position permitting rotation of the body relative to the coupling sleeve. A cam on the tightening sleeve is engageable with the locking member for displacing the locking member into the locking position when the coupling sleeve is in one of its end positions and for displacing the locking member into the freeing position when the coupling ring is in the other of its end positions. This structure allows the chuck to be locked.